The present invention relates to an image pickup apparatus and, more particularly, to an image pickup apparatus to be used upon being connected with a magnetic recording apparatus or monitor.
In conventional signal processing of an image pickup apparatus, a video signal (R/B and G signals) and a signal obtained by delaying this video signal by one horizontal (1H) period are input to a matrix processing circuit to obtain a luminance signal (Y) and color difference signals (R-Y and B-Y).
In this image pickup apparatus, to prevent MTF degradation, a low-pass filter is not arranged, and a video signal is delayed by one horizontal period by means of a delay means (e.g., a CCD drive type delay line, 1 HDL) without eliminating a clock component. The delayed signal is input to the matrix processing circuit. A clock component of the signal input to the delay means and a clock for driving the delay means are synchronized, as shown in FIGS. 1(a) to 1(d). The clock component (clock leakage amount) of the signal input to this delay means may be adversely affected by a preprocessing circuit and IC characteristics and may become a different clock component.
More specifically, the different clock components are exemplified as an R/B signal having a large magnitude shown in FIG. 1(a) and a G signal having a small magnitude shown in FIG. 1(b).
In this case, the levels of the R/B and G signals are detected as average value levels including the clock components (levels a and b in FIGS. 1(a) and 1(b). However, as the output from the delay means, the level at the phase of each sampling pulse becomes the output signal level. Therefore, the levels at the phases of the respective sampling pulses are detected as levels c and d in FIGS. 1(c) and 1(d), respectively.
Even if the levels of the R/B and G signals prior to the input to the delay means are set at the black level (non-signal level) (a=b), outputs from the delay means have a difference in black level (c.noteq.d). For this reason, errors occur in the Y, R-Y, and B-Y levels in the non-signal state, and a level difference occurs every 1H (first problem).
In the conventional image pickup apparatus, in order to obtain the luminance signal Y, the video signal (R/B and G signals) and the signal obtained by delaying this video signal by one horizontal period are added, and the added R/B and G signals are selectively output by a switching means. An LPF (Low-Pass Filter) for eliminating a leakage component of a CCD transfer pulse is arranged at the output of the CCD in the CCD 1H (horizontal scanning period) delay line used in the conventional image pickup apparatus. An 1H delay amount is obtained together with the delay amount of the LPF.
In the conventional delay line, however, since the delay amount of the LPF is included, a signal accurately delayed by 1H cannot be obtained.
If a color filter used in the CCD image sensor is constituted by G (green) stripes and R (red)/B (blue) line sequential arrangements, as shown in FIG. 2, a 1H delay line is required to generate a luminance signal by switching. Assume that output signals from the 1H delay line and the LPF connected to the 1H delay line when signals input to the 1H delay line are G(0) and R(0) shown in a timing chart of FIG. 3 are defined as G (-1) and B(-1), respectively. If the delay amount of the LPF has a correlation with gate pulses SWG and SWRB for the input signals G(0) and R(0) and a luminance signal SW-Y, as shown in the timing chart of FIG. 3, the SW-Y (luminance) output signal contains information of two pixels of the 1H delay line output by one switching operation, as shown in FIG. 3. For this reason, the resolution in the horizontal direction is degraded. At the same time, image degradation in the form of a moire is caused when the luminance signal Y is output (second problem).